A Baboon Has Survived Nearly 3 Years With A Pig's Heart, Suggesting Humans Could Too (Science Alert)"The baboon still had its original heart, so it wasn't relying on the pig's organ, but the fact that the heart survived inside its abdomen for so long without being destroyed by the monkey's immune system is impressive, and suggests that we could one day transplant animal organs into humans. Right now, 22 people die in the US every single day waiting for an organ transplant."

How Stuff Works: Allergies and Immune System (How Stuff Works)"Your immune system is your body's defense system against invading agents, such as bacteria, viruses, and parasites. These agents are called antigens. White blood cells are our main defense against these antigens. Your body makes many different types of white blood cells that work 24 hours a day to keep you healthy."

A Brief History of Cross-Species Organ Transplantation (NIH)"Cross-species transplantation (xenotransplantation) offers the prospect of an unlimited supply of organs and cells for clinical transplantation, thus resolving the critical shortage of human tissues that currently prohibits a majority of patients on the waiting list from receiving transplants. Between the 17th and 20th centuries, blood was transfused from various animal species into patients with a variety of pathological conditions."